A started transfer to the decarbonized power grids is based first of all on an increased use of the fossil fuels with reduced carbon content, such as natural gas (NG) in its gaseous and liquefied states. In the latter case an implication of the LNGSR terminals is constantly growing. As described in “Handbook of Liquefied Natural Gas” (by Saeid Makhatab, et al., Elsevier, Oxford, 2014), the LNGSR terminals perform the unloading and storage of the imported liquefied natural gas (LNG) and on-demand pumping, re-gasification and injection of the NO into transmission pipeline. According to report of the LNG-Worldwide Ltd. “Current Outlook for Global LNG to 2020 and European LNG Prospects” (September 2014), in 2013 the 104 existing LNGSR terminals in 29 countries have imported 237 MTPA of LNG fuel, providing at the time approximately 10% of the global gas consumption. Thereby, a volume of imported LNG is expected to grow by 2025 up to 500 MTPA.
On the other hand, a share of non-fossil and renewable (mainly wind and solar) energy sources in global electricity generation should be increased up to 11-12% by 2050 in the Blue Map scenario, according to “Prospects for Large-Scale Energy Storage in Decarbonized Power Grids”, Working Paper, IEA 2009, whereas in the EU countries the average level of 20% should be reached already in 2020. However with a large share of renewables in energy mix, it becomes vitally critical to ensure the on-demand and reliable supply of electricity, taking into account a variable output of the renewable energy sources and a frequent both positive and negative unbalance between this output and a current demand for power. One of the possible ways for solving this problem is the use of large-scale energy storages in the decarbonized power grids. According to the mentioned IEA estimates, an installed capacity of such energy storages should be increased from 100 GW in 2009 up to 189-305 GW by 2050. The large-scale energy storages could also solve a problem of operating the base-load (mainly coal and nuclear) power plants without significant reduction in the output of their steam generators during off-peak (low demand for power) hours in electrical grids.
Amongst the known methods for energy storage able to accumulate a lot of energy and store it over a long time-period, the recently proposed methods for Liquid Air Energy Storage (LAES) (see e.g. U.S. Pat. No. 9,638,068 and U.S. Patent Application No. 2017/0016577) are distinguished by the freedom from any geographical, land and environmental constraints, inherent in such other methods for large-scale energy storage technologies as Pumped Hydroelectrical Storage and Compressed Air Energy Storage. As described in the U.S. patent application No. 2017/0016577, the LAES method may comprise the following processes: forming a process air stream as the mixed stream of dry and CO2-free fresh air and recirculating air from the LAES system, compressing the process air in the multi-stage and intercooled compressor train with use of power from the electrical grid during LAES charge, liquefying a process air in the processes of its deep aftercooling, depressurizing a liquid air with forming the resulting charging liquid air and recirculating air, and storing the resulting liquid air in the storage tank with succeeding on-demand pumping, re-gasifying and expanding the stored air stream in the multi-stage expander train of the LAES system, accompanied by superheating and reheating a said air stream before and during its expanding with delivering the produced power into the electrical grid.
The LAES systems are characterized by much simpler permitting process and a possibility for co-location with any available sources of natural or artificial, cold or/and hot thermal energy, which may be used for enhancement of their power output and/or round-trip efficiency. One of such methods for integrations between the LAES system and the LNGSR terminal is described in the UK Patent Application No. GB 2512360, wherein a cold thermal energy of re-gasified LNG stream is proposed to use for significant reduction in power consumed during LAES charge mode. However, as evident from the report of Centre for Low Carbon Future “Liquid Air in the Energy and Transport Systems”, May 2013, a round-trip efficiency of the proposed integrated system still does not exceed 60-61%. This results from a not sufficiently recovered cold potential of the LNG stream and fully untapped cold potential of the process air escaped the LAES system during its discharge mode. In addition, in the discussed technical solution a provision was not made for conformity of the technological processes of the LAES charge and LNGSR terminal discharge, which may run at different times with use of ‘common-share’ equipment.
The further improvements in performance of the LAES system integrated with LNGSR terminal are necessary to increase a round-trip efficiency of non-fueled LAGES facility above 65% and a round-trip efficiency of fueled LAGES facility above 130%. At the same time a need for further improvement in other LAGES performance has been revealed. First and foremost, this is concerned with the necessity for tangible increase in specific discharge power of the fueled LAGES facility. This aim may be achieved through a decrease in relationship between the flows of LNG being re-gasified and charging air being liquefied, which presently exceeds 1.5:1. There is also a need for performing the whole cycle of LNG processing (preheating-evaporation-superheating) in the integrated LAES system to fully remove from service the terminal equipment during LAES charge. It is expedient also to profitably recover a waste cold of the re-gasified air stream and a waste heat of the power generation equipment used in discharge of the fueled LAGES facility. This will result in significant increase in the round-trip efficiency of energy storage, obviate a need for bulk and expensive cold and hot thermal energy storage and drastically increase a specific power of the LAGES facility which may be discharged for each MTPA of the LNG terminal send-out capacity.
Combining a number of the different processes related to two energy conversion methods (LAES and LNGSR) makes possible to significantly reduce the energy losses in both technological chains: electrical power—liquid air—electrical power and NG—LNG—NG and correspondingly improve the performance of both mentioned chains.